This application claims the benefit of Korean Patent Application No. 2000-7713, filed on Feb. 18, 2000, which is hereby incorporated by reference for all purposes as if fully set forth herein.
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device implementing an embossed reflective electrode.
2. Discussion of the Related Art
Recently, liquid crystal display (LCD) devices with light, thin, and low power consumption characteristics are used in office automation equipment and video units and the like. Such LCDs typically use a liquid crystal (LC) with an optical anisotropy. The LC has thin and long LC molecules, which causes an orientational alignment of the LC molecules. Therefore, the alignment direction of the LC molecules is controlled by applying an electric field to the LC molecules. When the alignment direction of the LC molecules for each pixel is properly adjusted by applying an electric field, the transmittance for each pixel is changed. Therefore, the LCD can display image data.
At this time, an active matrix (AM) LCD, where a plurality of thin film transistors (TFTs) and pixel electrodes are arranged in the shape of an array matrix, is widely used because of its high resolution and superiority in displaying moving pictures. When each TFT serves to switch a corresponding pixel, the switched pixel transmits an incident light in a normally-black mode LCD. Since an amorphous silicon layer is relatively easily formed on a large inexpensive glass substrate, an amorphous silicon thin film transistor (a-Si:H TFT) is widely used.
In general, liquid crystal displays are divided into transmissive LCD devices and reflective LCD devices according to whether the display uses an internal or external light source.
A typical transmissive LCD device includes a liquid crystal panel and a back light device. The liquid crystal panel includes upper and lower substrates with a liquid crystal layer interposed therebetween. The upper substrate includes a color filter, and the lower substrate includes thin film transistors (TFTs) as switching elements. An upper polarizer is arranged on the liquid crystal panel, and a lower polarizer is arranged between the liquid crystal panel and the backlight device.
The transmissive LCD device requires a high, initial brightness, and thus electrical power consumption by the backlight device increases. A relatively heavy battery is needed to supply a sufficient power to the backlight of such a device, and the battery can not be used for a lengthy period of time.
In order to overcome the problems described above, the reflective LCD has been developed. Since the reflective LCD device uses ambient light, it is light and easy to carry. In addition, the reflective LCD device is superior in aperture ratio to the transmissive LCD device.
FIG. 1 is a cross-sectional view illustrating a conventional reflective LCD device. As shown, between upper substrate 13 and lower substrate 11, a liquid crystal layer 19 is interposed, and between the liquid crystal layer 19 and lower substrate 11, a reflective electrode 16 is interposed. A common electrode 18 is interposed between the upper substrate 13 and liquid crystal layer 19, and on the exterior surface of the upper substrate 13, diffusing plate 21, retardation film 23, and polarizer 25 are sequentially formed.
The liquid crystal layer 19 has an optical anisotropy and controls the passage of light according to an electric field applied to the liquid crystal layer 19. A certain medium having a similar optical anisotropy may be used instead of the liquid crystal layer 19. The diffusion plate 21, retardation film 23, and polarizer 25 control the polarization state of light. Specifically, the diffusion plate 21 diffuses light to provide a wide viewing angle for users, while the retardation film 23 changes the polarization state of the incident light. In this case, a quarter-wave plate is used as the retardation film 23. The polarizer 25 transmits only rays parallel to a transmittance axis of the polarizer 25.
FIG. 2 is a plan view illustrating a pixel region of the conventional reflective LCD device. As shown, the pixel region xe2x80x9cPxe2x80x9d is defined by transverse gate line 33 and perpendicular data line 36, which cross each other. On the pixel region xe2x80x9cP,xe2x80x9d the reflective electrode 16 is formed, and at the cross point between the gate and data lines 33 and 36, a thin film transistor (TFT) xe2x80x9cTxe2x80x9d is formed as a switching device. The TFT xe2x80x9cTxe2x80x9d includes gate electrode 27, source electrode 29, and drain electrode 31. The source electrode 29 and the gate electrode 27 are electrically connected with the data line 36 and gate line 33, respectively. In addition, an active layer 30 is formed to overlap the gate electrode 27. The active layer 30 serves as a channel. Electric charges pass through the channel to transfer image data between the drain and source electrodes 31 and 29.
Still referring to FIG. 2, the reflective electrode 16 electrically contacts the drain electrode 31 via a drain contact hole 35. The reflective electrode 16 made of an opaque metal reflects an ambient light to the liquid crystal layer 19 (see FIG. 3). In addition, the reflective electrode 16 and common electrode 18 (see FIG. 3) apply electric signals to the liquid crystal layer 19 (see FIG. 3).
Now, with reference to FIG. 3, a fabricating process for the conventional reflective LCD device is explained. At first, on the lower substrate 11, a first metal is deposited and patterned to form the gate line 33 (see FIG. 2) and gate electrode 27 that is integrally protruded from the gate line 33. The first metal is selected from a group consisting of chromium (Cr), molybdenum (Mo), aluminum (Al), aluminum alloy, and tungsten (W).
Then, a gate-insulating layer 28 is formed on the lower substrate 11 to cover the gate line 33 (see FIG. 2) and gate electrode 27. The gate-insulating layer 28 is made of an inorganic insulating material, usually silicon oxide (SiOX) and silicon nitride (SiNX), or an organic insulating material, usually benzocyclobutene (BCB) and acryl.
On the gate-insulating layer 28, an amorphous silicon layer and a doped amorphous silicon layer are deposited and patterned to form the active layer 30 in an island shape. Thereafter, on the gate-insulating layer 28 where the active layer 30 is formed, a second metal is deposited and patterned to form the data line 36, source electrode 29, and drain electrode 31. The source electrode 29 is integrally protruded from the data line 36, and the drain electrode 31 is spaced from the source electrode 29. The second metal for the data line 36, and source and drain electrode 29 and 31 is usually the same material as the first metal for the gate line and gate electrode 27. Then, to cover the second metal layer, an organic insulating material, usually benzocyclobutene (BCB) or acryl is deposited as a passivation layer 36. The passivation layer 36 is patterned such that the drain contact hole 35 is formed over the drain electrode 31.
Thereafter, an opaque metal having a superior light-reflection property is deposited and patterned on the passivation layer 36 to form the reflective electrode 16 in the pixel region xe2x80x9cPxe2x80x9d of FIG. 2. As previously explained, the reflective electrode 16 electrically contacts the drain electrode 31 via the drain contact hole. Aluminum (Al) is conventionally used for the reflective electrode 16.
Thereafter, the lower substrate 11 is attached with the upper substrate 13 having the common electrode 18 on its inner surface, and the liquid crystal layer 19 is interposed between the upper and lower substrates 13 and 11. At this point, the diffusion plate 21 is conventionally formed on the exterior surface of the upper substrate 13. The diffusion plate 21 diffuses light such that high brightness and a wide viewing angle can be achieved.
However, due to the diffusion plate 21, the material cost of the LCD device increases.
FIGS. 4 and 5 show another conventional reflective LCD device. As shown in FIG. 4, a reflective electrode 17 having a plurality of concave portions 37a thereon is formed on the pixel region xe2x80x9cPxe2x80x9d. The concave portions 37a reflect incident light in various directions such that a diffusion effect can be achieved. With reference to FIG. 5, a fabricating process for the reflective LCD device of FIG. 4 is explained. After the source and drain electrodes 29 and 31 are formed via the same steps explained in FIG. 3, a passivation layer 38 is formed on the gate-insulating layer 28. The passivation layer 38 covers the source and drain electrodes 29 and 31. Then, the passivation layer 38 is patterned to have the drain contact hole 35 and concave portions corresponding to the concave portions 37a of FIG. 1. Thereafter, an opaque metal, usually aluminum is deposited and patterned on the passivation layer 38 including the concave portions. Therefore, the reflective electrode 17 having a plurality of concave portions 37a is formed on the pixel region.
In the above-described conventional reflective LCD device, the reflective electrode 17 serves to diffuse light, instead of the diffusion plate of the first conventional reflective LCD device shown in FIG. 3. Therefore, the material cost is relatively low.
However, due to the complicated patterning process for forming the concave portions 37a, the fabrication yield decreases. Further, since the size of the concave portion is limited, the diffusion effect by the concave reflective electrode is also limited.
Accordingly, the present invention is directed to a reflective LCD device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a reflective LCD device having an embossed reflective electrode.
In order to achieve the above object, a fabricating method for a liquid crystal display device includes: forming a gate line including a gate electrode on a substrate; forming a gate-insulating layer on the substrate, the gate-insulating layer covering the gate line and gate electrode; forming an active layer on the gate-insulating layer; forming a data line, a source electrode and a gate electrode on the active layer; forming a passivation layer on the gate-insulating layer, the passivation layer covering the data line, source electrode and gate electrode; dry-etching a surface of the passivation layer with gas such that the surface is embossed; and forming a reflective electrode on the embossed surface of the passivation layer such that an exterior surface of the reflective electrode is embossed.
The gas used for the dry-etching is beneficially a mixture gas of SF6+O2 or CF4+O2. Instead of the mixture gas, O2 gas can be used for the dry-etching.
The passivation layer preferably includes an organic insulating material, and the organic insulating material is preferably benzocyclobutene (BCB).
The reflective electrode is preferably an opaque conductive metal, and the opaque conductive metal is preferably an aluminum based metal.
In another aspect, the present invention provides a liquid crystal display device, which includes: upper and lower substrates with a liquid crystal layer interposed therebetween; gate line and gate electrode on the lower substrate; a gate-insulating layer on the lower substrate, the gate-insulating layer covering the gate line and gate electrode; an active layer on the gate-insulating layer; source electrode and drain electrode on the active layer; a data line on the gate-insulating layer; a passivation layer on the data line, source electrode, and drain electrode; and an embossed reflective electrode on the passivation layer.
The passivation layer preferably includes an organic insulating material, and the organic insulating material is preferably benzocyclobutene (BCB).
The reflective electrode is preferably an opaque conductive metal, and the opaque conductive metal is preferably an aluminum based metal.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.